Symptoms of thyroid problems include fatigue, weight gain, chills, hair loss, anxiety and excessive perspiration. The thyroid gland regulates the body's heart rate and plays a crucial role in its metabolism. Tel Aviv University researchers now think there may be another complication of thyroid imbalance: congenital deafness, according to an article in Mammalian Genome.
The study, which was supported by the National Institutes of Health and I-CORE Gene Regulation in Complex Human Disease, was conducted by Prof. Karen B. Avraham and Dr. Amiel Dror of the Department of Human Molecular Genetics and Biochemistry at TAU's Sackler School of Medicine using state-of-the-art imaging. The researchers found that congenital deafness can be caused by an absence of a thyroid hormone during development.
According to Dr. Dror, "Since our laboratory mainly focuses on the system of the inner ear, the study of a system such as the thyroid gland was new to us and therefore challenging. My curiosity as to how these two systems interact together to develop normal hearing led to this multidisciplinary study."
Using mouse populations, the researchers studied a form of congenital deafness that affects humans. Harnessing electron microscopy at the Sackler Cellular & Molecular Imaging Center, they tracked the inner hair cells of the cochlea (the auditory portion of the inner ear) in two groups - control (wild) mice and mutant (congenitally deaf) mice. They labeled inner-ear hair bundles in the affected mice with bright colors to highlight the disorganization of the ear's hair cells.
When the researchers examined the inner ear, they found a spectrum of structural and molecular defects consistent with hypothyroidism or disrupted thyroid hormone action. Analysis of the images revealed defective formation of the mice's thyroid glands: labeled thyroid follicles failed to grow or grew incompletely.
As Dr. Dror explained, "Our work demonstrated that normal hearing fails to develop when thyroid hormone availability is insufficient as a result of a genetic mutation. Our model provides a platform to test therapeutic approaches in order to prevent hearing loss before it occurs. There is still long way ahead before we get to the point of practical treatments with our research, but we believe we are moving in the right direction."
Dr. Dror said that his attraction to sound began very early as a child. He explained, "I play string instruments and pay great attention to sound quality and perception. As a graduate student in the Avraham laboratory, I was exposed to the fascinating world of genetics and the opportunity to combine two fields of research that I am interested in: genetics and hearing. Now that I have continued this research as a medical student, the direct interaction with patients with hearing impairments encouraged me to explore the clinical significance of my research."
As a physician, Dr. Dror believes it is important to pursue research with clinical consequences for his patients. He said, "The basis of all advanced medicine relies on both basic science and clinical research. I hope that our study will contribute a modest part to global efforts for improved medical care and treatment of hearing impairments."
Image: Cochlear Hair Cells